The present invention relates to a disk drive in which a disk is used as data-recording medium and the head writes data on the disk and read data from the disk. More particularly, the invention relates to a disk drive in which the head is retracted to a retract position.
A hard disk drive has a head and a head-retracting mechanism. The head is a slider having a read/write element, designed to write data on a disk and read data therefrom. The head-retracting mechanism retracts the head to a prescribed retract position when the disk is stopped and the head stops writing data on or reading data from the disk.
In a CSS (Contact Start and Stop) disk drive, the retract position is provided in the CSS area located at the innermost track of the disk. Thus, the head is retracted to the CSS area when the disk is stopped. The head, thus retracted, contacts the CSS area and remains in standby state. The head slides on the surface of the disk when the spindle motor provided in the disk drive starts rotating the disk and also when the spindle motor stops rotating the disk. The head may damage the disk, leaving xe2x80x9cscarsxe2x80x9d or the like on the surface of the disk. Therefore, the CSS area cannot be used as a data area, and is provided in a retract zone (also known as xe2x80x9cdedicated landing zonexe2x80x9d), which is distinct from the data zone. When the CSS disk drive is turned on, the spindle motor starts rotating the disk. As the spindle motor rotates the disk at high speed, an air bearing develops, which makes the head float above the disk. The head is moved from the retract zone to the data zone and positioned at a target position (i.e., a target track which the head will access to).
When the CSS disk drive is turned off or when a host system gives a command to the CSS disk drive to stop the spindle motor, the head is retracted to the CSS area and the spindle motor is stopped thereafter. When the head reaches the CSS area, the actuator supporting the head abuts on a stopper. The head is thereby prevented from jumping out of the CSS area. A voice coil motor (VCM) drives the actuator in the radial direction of the disk, moving the head in the same direction. The VCM so operates as it is supplied with a drive current from a VCM driver, which is controlled by the microprocessor (CPU) incorporated in the CSS disk drive.
The supply of power to the CSS disk drive may be abruptly stopped while the head is writing data on the disk or reading data therefrom. If this happens, the head must be retracted to the CSS area before the spindle motor stops. Unless the head is retracted so, it will collides with the disk when the disk creases to rotate while the head is floating above the data zone of the disk. Once the supply of power to the CSS disk drive is stopped, the VCM driver no longer supplies a drive current to the VCM. The actuator can not move the head at all.
In view of this, a new type of an HDD (Hard Disk Drive) has been developed. This HDD incorporates a reserve power supply having a capacitor (or a rechargeable battery). The capacitor is charged while the drive is being driven with the power supply (main power supply). When the main power supply is interrupted, power is supplied from the reserve power supply to the VCM, whereby the head is retraced. Another type of a disk drive has been developed, which has no reserve power supplies and in which the back electromotive force (EMF) generated as the spindle motor is driven is used to retract, the head.
Disk drives, known as xe2x80x9chead loading/unloading type,xe2x80x9d have been developed. Each disk drive of this type has a head loading/unloading mechanism. The head loading/unloading mechanism retracts the head to the retract position, unloading the head, whenever the disk stops rotating. At the retract position, a ramp is provided and supports the suspension of the actuator. When the disk acquires a normal rotation speed after it has started rotating, the head loading/unloading mechanism moves over the disk, loading the head. The mechanism prevents the head from contacting the disk, thus maintaining the surface smoothness of the disk and reducing the flying height of the head. This helps enhance the recording density of the disk.
As shown in FIG. 2, the head loading/unloading mechanism has a ramp (retract position) 14 located at the circumference of the disk 11. To unload the head, the actuator 13 is driven, moving the suspension 131. The head (slider) 12 supported by the suspension 131 is thereby moved to the ramp 14. As a result, the distal end of the suspension 131, to which a tab (not shown) is attached, then slides onto the inclined surface 141 of the ramp 14. The head 12 is thereby lifted above the surface of the disk 11. A stopper (not shown) stops the actuator 13 at a prescribed position outside the circumference of the disk 11.
During the normal operation of the disk drive, that is, while the disk drive is being supplied with power, the CPU incorporated in the disk drive controls, with high precision, the speed with which the actuator 13 is moved to unload the head 12. This is necessary, because if the speed is too high, the impact the suspension 131 exerts on the ramp 14 when it contacts the inclined surface 141 will increase, inevitably increasing the possibility that the disk 11 or the head 12, or both, are damaged.
The supply of power to the disk drive may be interrupted before the head 12 is unloaded (or retracted). If this happens, the disk 12 is stopped in the same way as in the CSS disk drive described above. Consequently, the head 12 collides with the disk 11. In order to prevent the collision, the disk drive of head loading/unloading type has a reserve power supply having a capacitor, just like the CSS disk drive. When the supply of power from the main power supply to the disk drive is interrupted, power is supplied from the reserve power supply to the VCM, which drives the actuator 13, thereby unloading. (retracting) the head 12.
With either the CSS disk drive or the head loading/unloading disk drive, it is possible to retract the head at an abrupt interruption of the supply of power, by means of the reserve power supply (including a back EME). Either disk drive is, however, disadvantageous in the following respects.
In a CSS disk drive containing a disk having a diameter of 2.5 inches, the reserve power supply supplies power to the VCM when the supply of power from the main power supply interrupted, as has been mentioned above. The head is thereby retracted, thanks to the use of the reserve power supply. The time required to retract the head from the data zone of the disk to the CSS area thereof is tens of milliseconds at most, even if the head is located at the outermost track, i.e., the remotest position from the CSS area. While the head is retracted, an almost constant current is supplied to the VCM from the reserve power supply. The value of the current depends on the capacitance of the reserve power supply. Driven by the VCM, the actuator moves the head. The speed at which the head is moved is proportional to the time required to retract the head from the data zone to the CSS area and is proportional to the square root of the distance the head is moved.
Assume that the CSS area, the innermost track and the outermost track have a radius of 15 mm, a radium of 16 mm and a radius of 31 mm, respectively. Then, the speed with which the actuator collides with the stopper when the head is retracted to the CSS area from the innermost track is about four times the speed with which the actuator collides with the stopper when the heat is retracted to the CSS area from the innermost track. Nonetheless, the speed with which the actuator collides with the stopper can be reduced to decrease the impact, because the actuator is driven with a relatively small current in the CSS disk drive. This speed should be of such a value as will cause the actuator to generate a force greater than the offset force of the FPC (Flexible Printed Circuit) board, which has terminals, connected to the head. The speed can be set at any desired value, only if the VCM-driving current is controlled by connecting a resistor in series the VCM. A head amplifier circuit is mounted on the FPC board, to amplify the signals the head reproduces from the disk. To accomplish stable operation of the CSS disk drive, it is desirable that the supply a smaller current to the VCM to retract the head from an outer track, than to retract the head from an inner track.
The two preceding paragraphs hold true of a head loading/unloading disk drive, too. In the head loading/unloading disk drive, however, the retract position (i.e., ramp 14) is located outside the circumference of the disk 11. Therefore, the speed with which the distal end of the suspension 131 contacts the inclined surface 141 of the ramp 14 when the head 12 is retracted from the innermost track is about four times the speed with which the distal end of the suspension contacts the surface 141 when the head 12 is retracted from the outermost track.
The friction generated while the distal end of the suspension 131 is sliding on the inclined surface 141 of the ramp 14 is greater than in the CSS disk drive. A large current must therefore be supplied to the VCM to retract the head 12 from an inner track of the disk, as well. In the head loading/unloading disk drive, the reserve power supply needs to have large capacitance to supply a relatively large current to the VCM when the supply of power from the main power supply is interrupted. However, the larger the current supplied to the VCM, the higher the speed with which the suspension 131 collides with the inclined surface 141 when the head 12 is retracted from the innermost track. The higher the speed, the greater the possibility that the suspension damages the head 12 or the disk 11, or both.
The object of the invention is to provide an apparatus and method which can reliably move the head in a disk drive, to a retract position at an appropriate speed, when the supply of power to the disk drive is interrupted.
To attain the object, an apparatus for retracting a head on power down in a disk drive, which comprises: an apparatus for retracting a head from a disk surface on power down in a disk drive, comprising: actuator means supporting head and designed to move the head form a retraction position to a prescribed area on the disk; reserve power means provided apart from a main power supply to the disk drive, for supplying a drive current to the actuator means when supply of power from the main power supply is interrupted; retract means for calculating a distance for which the head is to be moved to the retract position, from a present position of the head, and for determining a control value corresponding to the distance calculated; and control means for controlling the drive current supplied from the reserve power means to move the head to the retract position, on the basis of the control value determined by the retract means.
The actuator means has a voice coil motor (VCM) and moves the head at the speed corresponding to the drive current supplied to the VCM. The retract means calculates the distance the head should be moved to the retract position by using the reserve power means when the supply of power from the main power supply is interrupted. Further, the retract means determines the control value for setting a drive current for the VCM, from the distance it has calculated. The control means controls the drive current supplied to the VCM from the reverse power means, in accordance with the control value determined by the retract means.
When the supply of power from the main power supply is abruptly interrupted while the head remains above the disk, the head can be moved from the disk surface to the retract position by means of the reserve power means. The control means calculates the distance the head must be moved to the retract position and sets a drive current for the VCM, from the distance calculated. Hence, the head can be retracted at an appropriate speed, not at an excessively high speed. In short, the head is moved to the retract position, such as a ramp, at an appropriate speed, not merely by using the reserve power means, at the interruption of the supply of power from the main power supply. Thus, the head can be reliably retracted, not being damaged or damaging the disk.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.